Conventional conveyor belts which are used in heavy duty applications are typically comprised of a cured rubber as a top layer, a cured rubber as a bottom layer, and a fabric reinforcement layer (a carcass) which is sandwiched between the top layer and the bottom layer. Rubber conveyor belts of this type can offer excellent performance characteristics and a relatively long service life. However, rubber conveyor belts are labor intensive to manufacture and require a curing step wherein the rubber components of the belt are cured (vulcanized) into their final form to produce the belt as a finish product.
The utilization of polyvinylchloride plastisols in adhering various components of the fabric reinforcing carcass used in conveyor belts is known in the art. For instance, U.S. Pat. No. 4,813,533 discloses a flat belting which includes a plurality of individual layers of fabric that extend throughout the length and width of the belting. The layers are joined together by reinforcing elements which extend substantially in the direction of the thickness of the belting. The individual layers and reinforcing elements are encapsulated in a matrix of polymeric elastomeric resin, for example, polyvinylchloride. The individual layers are saturated with a liquid elastomer-forming polymeric resin prior to their being joined together. The reinforcing elements may be inserted, for example, by tufting, sewing, or stitch-bonding. One or more of the individual fabric layers may be a woven or other cloth having a plurality of substantially parallel yarns which extend in the lengthwise direction of the belting. One or more of the individual fabric layers may be a non-woven fabric. In cases where the liquid saturate is a polyvinylchloride plastisol, the resin is gelled by application of heat. The term “gelling” as used in U.S. Pat. No. 4,813,533, means that the polyvinylchloride plastisol becomes solid and will not thereafter flow at room temperature but its physical properties are not yet fully developed. In any case, this reference indicates that gelling of polyvinylchloride plastisol can be accomplished by heating the liquid plastisol to temperature of at least 200° F. (93° C.) to 220° F. (104° C.).
U.S. Pat. No. 4,928,812 discloses a conveyor belt, which has a high strength, tear resistance and flame retardancy, and which is particularly suitable for use in coal mines. It comprises a matrix of thermoplastic elastomer resinous material, e.g., PVC, reinforced with an armouring comprising a layer of primary tension elements extending substantially rectilinearly in the longitudinal direction of the belt and consisting of continuous filaments, and covering layers consisting of yarns or threads disposed on both sides of the primary tension elements so as to impart coherence in the transverse direction of the belt, the top and bottom covering layers being connected by tying yarns or threads. The primary tension elements are composed of cables or cords of aramid. Adjacent primary tension elements are separated by gaps having a width of 0.5 to 3 times, more particularly 2 times the outer diameter of the primary tension elements. The gaps are filled up with one or more elements such as, e.g., cotton cables or cords. U.S. Pat. No. 4,928,812 more specifically reveals a conveyor belt comprising: (I) a matrix based on polyvinylchloride; and (II) a reinforcing construction embedded in said matrix, said reinforcing construction comprising a compound woven fabric including: (a) a first layer including (i) a plurality of primary load-bearing warp members each formed by a plurality of substantially parallel cables or cords of continuous filaments of aramid and extending rectilinearly in a longitudinal direction of the belt, each of said primary load-bearing members having an outer diameter D, adjacent ones of said primary load-bearing members being spaced apart from one another to form spaces there between having a width which is 0.5-2.0 times said outer diameter D of said primary load-bearing members and (ii) a plurality of second nonaramid cotton comprising filling warp members respectively disposed rectilinearly in said spaces between said primary load-bearing members; (b) a second layer provided on an upper side of said first layer and a third layer provided on a lower side of said first layer, said second and third layers each comprising cotton yarns adhered to said polyvinylchloride matrix; and (c) a plurality of binder warp yarns or filaments which interconnect said first layer, said second layer and said third layer.
There remains to be a long felt need for a technique of manufacturing conveyor belts which are free of rubbery polymers which require a cure cycle and that provide excellent performance characteristics and with a good service life. However, inadequate ply adhesion has been a problem that has stood in the way of such an advance in the state of the art.